Infections are serious complications of ophthalmic implant surgery. Examples of ocular implants include intraocular lenses, glaucoma valves, and artificial corneas, which are also known as keratoprostheses. An uncontrolled infection after ophthalmic implant surgery of any of these devices can result in loss of vision or even loss of the eye.
It is important to distinguish ophthalmic implants from contact lenses. Although both are considered medical devices, their purpose and requirements for proper functioning are very different.
Contact lenses are clear lenses that float on the human tear film. They are not physically attached to the eye in any way and direct contact between the contact lens and tissue is known to cause complications including corneal abrasions, infections and corneal scarring. A contact lens' purpose is to refract light to allow proper focus of light rays onto the retina.
By contrast, an ophthalmic implant is any device; clear, translucent or opaque, that can be embedded inside ocular tissue. An ophthalmic implant must be biocompatible with the ocular tissues in order to function.
The most common strategy used in reducing the risk of infection after ophthalmic implant surgery is the use of topical antibiotic drops. However, this regimen has the significant disadvantage of needing to rely on the patient's compliance to insure that the medications are dosed properly. The infection issue is especially troublesome in the case of artificial cornea implants, which currently require the daily administration of topical antibiotics drops for the life of the patient. The use of such antibiotics is necessary because current artificial corneas are exposed to the non-sterile surface of the eye. As such, there is a continual risk of infection.
Other inventors have recognized the inadequacy of antibiotic medications as a method of reducing infection after ophthalmic implant surgery. One alternative strategy that has been proposed is to either coat or covalently bond antibacterial chemicals to the surface of the ophthalmic implant as disclosed in U.S. Pat. No. 6,976,997 issued to Noolandi et al. A limitation of this method is that coatings and covalently bonded chemicals can be eroded away from the surface of the implant over time. Therefore, it is predictable that the antibacterial properties of these types of implants will decrease over time thereby increasing the risk of infection.
Another strategy, which has been proposed in the past, is to infuse the polymer of the ophthalmic implant with an antibacterial metal ion. In particular, silver and copper metal have been proposed as agents to be infused into polymers for use in an ophthalmic implant. Although, the use of free metal ions as an antibacterial agent within polymers has been used widely in commercial plastic goods and in some short-term disposable medical devices such as catheters, metal ions are known to be dangerous in the eye.
Argyrosis is the medical term for silver toxicity of the eye. Argyrosis has been reported to result in a slate gray discoloration of the conjunctiva and iris. Argyrosis has also been found to result in cataracts and retinal maculopathy, both of which are vision threatening conditions.
Copper toxicity in the eye results in a characteristic green ring around the cornea, which is termed a Kayser-Fleischer ring. Moreover, studies have demonstrated that copper toxicity can induce ocular complications such as intraocular inflammation (uveitis), hemorrhage, vitreous liquefaction, hypotony, iris ischemia and retinal damage.
In addition, free metal ions may also leach out of the polymer over time and therefore, the polymer may lose its antimicrobial properties over time.
For the stated reasons, there remains a need in the art for an improved composition and method of decreasing the risk of microbial infections after ophthalmic implant surgery.